This application is based on and claims priority under 35 U.S.C. .sctn. 119 with respect to Japanese Application No. 2002-57471 filed on Mar. 4, 2002, the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a crankpin lathe for machining or turning each of crankpins on a crankshaft with a cutting tool with each such crankpin being kept aligned with a rotating work spindle and being rotated therewith. The present invention also relates to a tool head and a work head for the crankpin lathe.
2. Discussion of the Related Art
A crankpin lathe is described in Japanese Unexamined Published Patent Application No. 08-11001 having a device for rotationally indexing a crankshaft for a four-cylinder engine through 180 degrees with respect to a work spindle for the purpose of bringing each of unfinished crankpins into alignment with the axis of the work spindle for driving the crankshaft. In the known lathe, when the indexing is to be done, a work shifting mechanism grasps the crankshaft, and chucks of work spindles for clamping journals of the crankshaft are opened to release the same. Then, the work spindles are rotationally indexed through 180 degrees, and the work shifting mechanism is moved together with the crankshaft twice the eccentricity of the crankpins in the radial direction of the work spindles to bring an unfinished crankpin in axial alignment with the work spindles, whereafter the chucks are closed to grasp the journals.
However, in the aforementioned known lathe, the rotational indexing of the crankshaft with respect to the work spindles unavoidably involves extracting the end journals from the chucks with the crankshaft being held by the work shifting mechanism, rotating the crankshaft through 180 degrees, operating the work shifting mechanism to move through a distance corresponding to twice the eccentricity of the crankpins in the radial direction, and then, inserting the journal into the chuck to clamp the same. This disadvantageously causes a substantial time to be consumed for positioning a crankpin to be machined next onto the axis of the work spindle. Further, since the chucks are opened to release the crankshaft whenever the machining of one or more crankpins at the same angular phase is finished, another problem occurs in that relative rotation takes place between the crankshaft and the work spindle thereby to cause an error in positioning other crankpins on the axis of the work spindle. In addition, the work shifting mechanism for grasping the crankshaft to transfer disadvantageously causes the apparatus to be enlarged in configuration and increased in manufacturing cost.
It is therefore a primary object of the present invention to provide an improved crankpin lathe capable of overcoming the drawbacks of the prior art crankpin lathe.
Another object of the present invention is to provide an improved crankpin lathe capable of rotationally indexing a crankpin to be machined next onto the axis of a work spindle speedy and precisely.
A further object of the present invention is to provide an improved tool head and an improved work head which are particularly advantageous when incorporated into the crankpin lathe according to the present invention.
Briefly, in a crankpin lathe as defined in claim 1 according to the present invention, work heads are mounted on a bed for supporting work spindles driven by work spindle drive devices, respectively; the work spindles are provided for clamping journals of a crankshaft thereon with a crankpin being positioned on the rotational axis of the work spindles; and a tool head for attaching cutting tools is mounted on the bed to be moved by a tool head feed device relative to the work heads for turning the crankpin. The crankpin lathe further comprises index members supported respectively on the work spindles for rotation about an axis which is parallel with, and offset by an eccentricity of the crankpins, from the axis of the work spindles; clutch mechanisms each interposed between the rotary member and the work spindle for restraining the relative rotation between the rotary member and the work spindle when brought into engagement, but for permitting the relative rotation when released from engagement; and clamp devices provided respectively on the work spindles for removably clamping the journals. The crankpin lathe further comprises a pin pusher mounted on the bed and movable by a pin pusher feed device toward the axis of the work spindle for causing the pin pusher to push the crankpin; and a control device for positioning the machined crankpin to a position spaced by a predetermined distance from the axis of the work spindles by pushing with the pin pusher the machined crankpin with the clutch device being made disengagement and for rotating the work spindle by half an angle through which the crankshaft is to be indexed rotationally relative to the work spindles so as to position a crankpin to be machined next onto the axis of said work spindles before bringing the clutch device into engagement.
With the configuration as defined in claim 1, the journals of the crankshaft are clamped on the index members supported rotatably about an axis which is parallel with, and offset by the eccentricity of the crankpins from, the work spindle axis. In this state, the clutch device interposed between the work spindle and the index member is brought into disengagement, the pin pusher is advanced and pushes the machined crankpin to a position spaced by a predetermined distance from the work spindle axis, and the work spindle is rotated by half the rotational angle through which the crankshaft is to be rotationally indexed, so as to position a crankpin to be machined next onto the work spindle axis, whereafter the clutch device is brought into engagement. Therefore, it can be realized to position the crankpin precisely onto the work spindle axis within a short period of time using the mechanisms which is simple in construction and low in cost.
In another aspect as defined in claim 6 of the present invention, there is provided a crankpin lathe of the same character and configuration noted above except that a single work head is provided rather than the double work head construction noted above. This configuration with the single work head is applicable to those crankshafts which are short in length for use in engines for compact cars, motorcycles, home-use compressors, home-use power generators or the like.
In a further aspect as defined in claim 7 of the present invention, there is provided a tool head for a crankpin lathe wherein a crankshaft is clamped on at least one work spindle rotatably carried on a work head, with a crankpin to be machined next being in axial alignment with the axis the work spindle so that the crankpin is machined with a cutting tool moved radially thereof while being rotated about the axis of the work spindle. The tool head comprises a tool head body mounted to be movable in a first direction parallel with the axis of the work spindle and a second direction transverse to the axis of the work spindle; first and second feed devices drivingly connected with the tool head body for moving the same respectively in the first and second directions, a plate-like index body carried on the tool head body and rotationally indexable about an axis parallel with the axis of the work spindle. The index body has a thickness larger than the distance between a pair of shoulder surfaces formed on axial opposite ends of the crankpin to be machined. The tool head further comprises an index drive device provided on the tool head body for rotationally indexing the index body; and a plurality of tool attaching portions arranged on the circumferential portion of the index member for respectively attaching cutting tools thereon and formed as locally thin portions whose width is narrower than the distance between the pair of shoulder surfaces, so that each of the locally thin portions is able to advance between the pair of shoulder surfaces without interfering with the same.
In this construction, the tool attaching portions are made narrower than the distance between the pair of shoulder surfaces of each crankpin and can be advanced between the pair of shoulder surfaces without interfering with the same. Consequently, the length through which each cutting tool protruded from the circumferential surface of the index body can be shorted whereby the rigidity in supporting the cutting tool on the index body and hence, the machining accuracy can be improved.
In a still further aspect as defined in claim 9 of the present invention, there is provided a work head for a crankpin lathe wherein a work spindle clamping thereon a crankshaft is rotated with a crankpin to be machined being in axial alignment with the axis of the work spindle. The work head comprises the work spindle rotatably supported in a housing of the workpiece; a chuck body connected with one end of the work spindle; an index member mounted in the chuck body with the axis thereof being offset by the eccentricity of the crankpin from the axis of the work spindle and rotatably indexable about the axis thereof; a collect chuck co-axially received in the index member and rotatable bodily therewith. An operating mechanism is received in the work spindle and is connected with the collet chuck for operating the same so as to clamp a journal of the crankshaft on the work spindle, and a clutch mechanism is interposed between the chuck body and the index member for selectively making the same freely rotatable or restrained from free rotation. A servomotor for rotating the work spindle with the clutch mechanism being disengaged is further provided, whereby relative rotation between the work spindle and the crankshaft is brought about thereby to rotationally index a crankpin onto the axis of the work spindle.
With the construction as constructed above, when the crankshaft is to be indexed, the clutch mechanism is disengaged to make the crankshaft rotatable freely relative to the work spindle. However, the crankshaft is kept clamped by the collet chuck during being indexed. Therefore, the deviation in angular position of the crankshaft relative to the work spindle can be avoided so that no error is involved in the machining accuracy. Moreover, the indexing of the crankshaft is carried out with an end part of the crankshaft being inserted into the collect chuck, no step is taken to extract the end part of the crankshaft from the collect chuck in advance of the indexing rotation, so that the time for the indexing operation can be shortened.